1. Field of the Disclosure
The present embodiments relate to semiconductor substrate processing methods and equipment tools, and more particularly, atomic layer deposition (ALD) systems that enable spatial ALD with a moving RF source.
2. Description of the Related Art
Atomic layer deposition (ALD), also known as atomic layer chemical vapor deposition (ALCVD), is a method for producing very thin films that are highly conformal, smooth, and possess excellent physical properties. ALD uses volatile gases, solids, or vapors that are sequentially introduced (or pulsed) over a heated substrate. A first precursor is introduced as a gas, which is absorbed (or adsorbed) into the substrate and the reactor chamber is cleared of the gaseous precursor. A second precursor is introduced as a gas, which reacts with the absorbed precursor to form a monolayer of the desired material. By regulating this sequence, the films produced by ALD are deposited a monolayer at a time by repeatedly switching the sequential flow of two or more reactive gases over the substrate.
Throughput of the typical ALD system is limited. The limitations of gas switching technology, as well as the time required to purge the single substrate showerhead and reactor introduce inherent delays.
One type of emerging atomic layer deposition (ALD) reactor is spatial ALD wherein rather than bringing reactants to the substrate, the substrate is brought to the reactants instead. In spatial ALD schemes that involve a plasma in the frame of the substrate, the plasma moves onto and over the substrate from a source that is non-moving and fixed in an inertial frame of reference. Such reactors leave the plasma on during substrate transfer, as each reaction zone in the special ALD reactor has its own RF power source. As this plasma front moves over the substrate, it can induce currents that can lead to device damage.
Spatial ALD systems also suffer in that deposited materials over the leading edge of the substrate, due to longer residence time under the plasma, may become thicker (e.g., tilt in the deposition layer) than the trailing edge of the substrate. Another problem is that the trailing edge can be exposed to the precursor and also byproducts. Still another drawback from such spatial ALD schemes is that internal feature deposition may be non-uniform, wherein inert feature sidewalls build-up with different thicknesses. In these systems, there is also a reported thickness variation that manifests itself in an asymmetric film thickness inside of features. And in some cases, film damage occurs. Film damage occurs due to excessive ion bombardment which may not be uniform across the wafer. The asymmetric profiles within the feature are more of an issue inboard to outboard in systems where the wafer is rotated about a remote center, circumscribing an arc. Despite best efforts to minimize damage and/or non-uniform deposition profiles, such spatial ALD schemes still suffer.
It is in this context that disclosures arise.